Accommodation is the ability of the eye to change the power of the eye to enable clear vision with objects in focus for a range of distances. With a change in focus from distance to near vision, the ciliary muscle contracts, the zonules (filaments that connect the crystalline lens to the ciliary muscle) relax and the crystalline lens takes a more rounded form resulting in an increase in power and resulting in the ability of the eye to focus on near objects. However, with age, there is a gradual decline in the accommodative power of the eye due to the crystalline lens losing its flexibility in changing its shape and in humans, in their forties this results in blurred vision for near tasks such as reading and is called Presbyopia. The condition is commonly managed with glasses or contact lenses.
In those that have cataracts, the crystalline lens is extracted and an intraocular lens is commonly implanted. Typically, the intraocular lens is a fixed focus lens that enables the eye to see distant objects. Since the implanted lens is unable to change shape and thus a change in power, the condition typically necessitates the use of spectacle lenses to be able to see at near. In both these situations, i.e. in presbyopia and following cataract extraction, the desire is to eliminate or reduce the need for spectacles for near distances and restore the accommodative power i.e. the re-establishment of the eye's ability to focus for a range of distances.
While many approaches have been explored, the development of a flexible material that would replace the natural material of the crystalline lens and fill the capsular bag and provide accommodation is highly desired. For example, two part silicone elastomers (referred to as RTV or LTV silicones) require a polyfunctional vinyl siloxane as one component and a polyfunctional hydrosiloxane silicone polymer as the other component and cure at body temperature via platinum catalysed hydrosilation reaction. However, these compositions suffer from the need to mix the two polymers immediately prior to injection and introduced into the capsular bag before the viscosity of the composition rises too far. Another approach is based on use of compositions of polysiloxanes with photocurable moieties, however it has been said that the modulus of the cured composition is too high to restore accommodation. Another approach involves hydrogel compositions that offer access to low modulus compositions but involve UV curing that poses a problem with respect to their safety for surrounding tissues. Also the resultant cured composition did not achieve the desired refractive index to provide for the accommodative power and also suffered from post cure swelling.
Thus there is a continued demand for compositions and methods that are disclosed herein. For example, compositions suitable for injection into the capsular bag of the eye of a warm blooded animal and are able to be cured in situ and allow for restoration of accommodative power.
Reference to prior art in this specification is not, and should not be taken as acknowledgement or form of suggestion that this prior art forms part of the general knowledge in Australia or other jurisdictions or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by person skilled in the art.